refactor(baseline syslinux)!: restructure syslinux configuration for multi-boot selection

Replace simple serial-based menu with system detection logic using whichsys.c32 to automatically select between PXE and direct system boot. This enables dynamic boot method selection while maintaining support for both boot scenarios.

BREAKING CHANGE: Changes syslinux.cfg structure from single menu-based boot to conditional boot selection. Systems relying on the previous serial menu interface and default 'arch' label will need to adapt to the new whichsys-based selection mechanism.

configs/baseline/syslinux/syslinux.cfg

@@ -1,9 +1,11 @@
-SERIAL 0 115200
-UI menu.c32
-MENU TITLE Arch Linux
-MENU CLEAR
+DEFAULT select
 
-DEFAULT arch
-TIMEOUT 30
+LABEL select
+COM32 whichsys.c32
+APPEND -pxe- pxe -sys- sys -iso- sys
 
-INCLUDE syslinux-linux.cfg
+LABEL pxe
+CONFIG archiso_pxe.cfg
+
+LABEL sys
+CONFIG archiso_sys.cfg